Inorganic phosphate corrosion resistant coatings

ABSTRACT

This disclosure relates to phosphate coatings that inhibit corrosion of metals, specifically coatings comprising acidic phosphate and alkaline metal oxide/hydroxide components. In one particular embodiment, phosphate-based coating formulations that reduce or eliminate corrosion of steel and other metals are disclosed. In other embodiments, methods for coating steel surfaces with acidic phosphate and alkaline metal oxide/hydroxide components to reduce or eliminate corrosion of the metal surfaces are disclosed.

The present application is a divisional of U.S. application Ser. No.12/860,513, filed August 20, 2010, which claims the benefit of U.S.Provisional Application Nos.: 61/285,948 filed Dec. 11, 2009 and61/288,192 filed on Dec. 18, 2009, the entire contents of each beingincorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to coatings comprising acidic phosphate andalkaline metal oxide/hydroxide components that inhibit corrosion ofmetals, and specifically, the manufacture and method of coating onmetal.

BACKGROUND

Corrosion of structural steel and other metals is a serious problem inconstruction and utility industry. When exposed to humid and salineenvironments, especially at elevated temperatures, steel deteriorates.To minimize or reduce the extent of this corrosion, alloys of steel,such as galvanized (zinc coated) compositions, or chrome platedcompositions are used. While this approach may solve the problem in theshort run, the problem persists when the steel is exposed to theabove-mentioned environments over long periods of time. This inventiondiscloses uniquely-suited phosphate-based composite coatings thatminimize or reduce the corrosion of steel or other metals and make itunnecessary to use alloys of steel such as galvanized (zinc coated)compositions or chrome plated compositions.

Phosphating to passivate a steel surface is generally known in the steelindustry. Typically, well polished steel is immersed in phosphate bathof pH between 4-4.5 containing 2-3 g/L phosphoric acid, 2-3 g/L ofammonium or zinc dihydrogen phosphate as buffer, and a small amount(<0.5 g/L) of oxidizer, to produce an iron phosphate passivation layer.In the process, however, hydrogen gas is liberated by the reaction ofelemental iron with water in the extremely acidic environment. Thisproduces a very thin passivation layer that is porous and not abrasionresistant, and as a result, an additional coating is required to makethe surface of the passivated steel inaccessible to atmospheric oxygen.This process has, therefore, at least the following disadvantages: (i)an acid immersion bath/tank, which generates sludge as formed byaccumulating reaction products—making the bath less effective andcreating environmental disposal issues for the sludge and the acidicsolution; (ii) oxidizers used in the passivation process produce toxicgases. For example, chlorates produce chlorine, meta nitro benzenesulfonic acid produces nitrous oxide, potassium permanganate presentsoccupational health risks; (iii) resultant passivation layers are notabrasion resistant, therefore, abrasion resistance must be augmented byadditional coating(s).

SUMMARY

In a first embodiment, a method for preventing or reducing corrosion ofa corrodible metal surface is provided. The method comprises contactingthe corrodible metal surface with a mixture of an acidic phosphatecomponent and a basic component comprising at least one of a metaloxide, a basic metal hydroxide, or basic mineral. In addition tocorrosion resistance, improved abrasion resistance is also obtainedusing the compositions and methods herein disclosed.

In a first aspect of the first embodiment, the acidic phosphatecomponent is phosphoric acid, alkali metal dihydrogen phosphate MH₂PO₄,alkali earth dihydrogen phosphate M(H₂PO₄)₂ or its hydrate, transitionmetal trihydrogen phosphate MH₃(PO₄)₂ or its hydrate, or mixturesthereof.

In a second aspect, alone or in combination with any one of the previousaspects of the first embodiment, the acidic phosphate component is monopotassium phosphate or its hydrate.

In a third aspect, alone or in combination with any one of the previousaspects of the first embodiment, the basic component is at least one ofmagnesium oxide, barium oxide, zinc oxide, calcium oxide, copper oxide,iron oxide, and hydroxides thereof, or magnesium brine containing aneffective amount of magnesium hydroxide.

In a fourth aspect, alone or in combination with any one of the previousaspects of the first embodiment, the basic component is at least one ofmagnesium oxide and magnesium hydroxide.

In a fifth aspect, alone or in combination with any one of the previousaspects of the first embodiment, the acidic phosphate component is monopotassium phosphate or its hydrate, and the basic component is magnesiumbrine having a pH of about 9 to about 11, wherein the magnesium brinecontains an effective amount of magnesium hydroxide.

In a sixth aspect, alone or in combination with any one of the previousaspects of the first embodiment, the mixture of acidic phosphatecomponent and basic component forms at least one of magnesium potassiumphosphate, magnesium sodium phosphate, magnesium hydrogen phosphate,copper hydrogen phosphate, zinc hydrogen phosphate, barium hydrogenphosphate, or iron hydrogen phosphate.

In a seventh aspect, alone or in combination with any one of theprevious aspects of the first embodiment, the surface is steel oraluminum.

An eighth aspect, alone or in combination with any one of the previousaspects of the first embodiment, further comprises producing on thecontacted corrodible surface a magnesium-glass-phosphate, glossycoating.

In a ninth aspect, alone or in combination with any one of the previousaspects of the first embodiment, the contacting is with a slurry, paste,spray, or vapor thereof, independently, of the acidic phosphatecomponent or the at least one of the basic metal oxide or the basicmetal hydroxide component.

In a second embodiment, a corrosion-inhibiting coating composition isprovided. The coating composition comprises a slurry of a combination ofone or more iron oxides with magnesium dihydrogen phosphate.

In a first aspect of the second embodiment, the iron oxide is a mixtureof magnetite (Fe₃O₄) or wustite FeO, and hematite (Fe₂O₃). In anotheraspect, the total amount of hematite used is greater than the amount ofmagnetite or wustite.

In a third embodiment, a method is provided, the method comprisingcontacting a corrodible surface with coating consisting essentially of amixture of magnetite or wustite, and hematite; with a solution ofphosphoric acid or magnesium dihydrogen phosphate, wherein thecorrodible surface is essentially without a primer layer; and providinga corrosion-inhibiting coating, the coating comprising iron hydrogenphosphate.

In a fourth embodiment, a method of providing corrosion inhibition isprovided. The method comprises providing a combination of at least oneof the following: (i) magnesium oxide (MgO) and mono potassium phosphate(KH₂PO₄); (ii) magnesium oxide (MgO) and phosphoric acid solution (H₃PO₄solution); (iii) magnesium oxide (MgO) and magnesium dihydrogenphosphate; (iv) ferric oxide (Fe₂O₃) and phosphoric acid (H₃PO₄); (v)magnesium brine containing an effective amount of magnesium hydroxideand mono potassium phosphate (KH₂PO₄); (vi) magnesium brine containingan effective amount of magnesium hydroxide and phosphoric acid (H₃PO₄);or (vii) magnesium brine containing an effective amount of magnesiumhydroxide and magnesium dihydrogen phosphate; and contacting the surfaceof a corrodible metal with at least one of the combinations (i)-(vii).

In a first aspect of the fourth embodiment, the combination is presentedas a slurry, paste, spray, or vapor.

In a fifth embodiment, an article comprising a corrosion-inhibitingcoating formed by the combination of an acidic phosphate with a basicmetal oxide or basic metal hydroxide is provided.

In a first aspect of the fifth embodiment, the coating is at least oneof magnesium potassium phosphate, magnesium sodium phosphate, magnesiumhydrogen phosphate, barium hydrogen phosphate, copper hydrogenphosphate, zinc hydrogen phosphate, or iron hydrogen phosphate.

In a second aspect, alone or in combination with any one of the previousaspects of the fifth embodiment, polyphosphates are present at theinterface of the article surface and the corrosion-inhibiting coating.

In a third aspect, alone or in combination with any one of the previousaspects of the fifth embodiment, magnesium chromates are present at theinterface of the article surface and the corrosion-inhibiting coating.

In a sixth embodiment, a steel or iron-based article having a coatingcomprising a berlinite phase (AlPO₄) detectable by x-ray diffraction isprovided.

In a seventh embodiment, a method is provided. The method comprisescontacting a previously corroded surface overlaying a metal with acomposition comprising a mixture of an acidic phosphate and a basicmetal oxide or a basic metal hydroxide, wherein an excess of thecomposition and a portion of the previously corroded surface is renderedreadily removable and/or dislodges from the surface.

A first aspect of the seventh embodiment, further comprises forming athin, corrosion protection layer on the surface.

In a second aspect, alone or in combination with any one of the previousaspects of the seventh embodiment, wherein the mixture provides at leastone of magnesium potassium phosphate, magnesium sodium phosphate,magnesium hydrogen phosphate or iron hydrogen phosphate to the metalsurface.

In a second aspect, alone or in combination with any one of the previousaspects of the seventh embodiment, the corrosion protection layer iscapable of self regenerating the corrosion protection layer from defectsformed therein.

In any of the first, second, third, fourth, fifth, sixth or seventhembodiment, alone or in combination with any of their respectiveaspects, methods and articles of improved abrasion resistance or incombination, improved corrosion and abrasion resistance is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of the redox potential vs. pH diagram for ironshowing passivation and corrosion regions and comparing conventionalphosphate coating and the methods disclosed and described herein.

FIG. 2 is an X-ray diffraction pattern diagram illustrating a corrosionprotection layer of a coating composition as disclosed and describedherein.

FIG. 3 is an X-ray diffraction pattern diagram illustrating a coatingcomposition as disclosed and described herein.

FIG. 4 is an X-ray diffraction pattern diagram illustrating a coatingcomposition as disclosed and described herein.

FIG. 5 is SEM image illustrating a coating composition as disclosed anddescribed herein.

FIG. 6 is SEM image illustrating a coating composition as disclosed anddescribed herein.

FIG. 7 is SEM image illustrating a coating composition as disclosed anddescribed herein.

FIG. 8 is SEM image illustrating a coating composition as disclosed anddescribed herein.

FIG. 9 is diagram illustrating a self-regenerating coating as disclosedand described herein.

FIG. 10 is a Raman spectrograph of a coating as disclosed and describedherein.

DETAILED DESCRIPTION

The uniquely-suited formulations and methods disclosed and describedherein are based on acid-base inorganic phosphate compositions. Examplesof the coatings provided herein include magnesium potassium phosphatecoating, and iron hydrogen phosphate coating. These compositions areused as coatings on steel and other metals as corrosion inhibitors. Whenapplied to a metal surface as a coating, the paste formed by any ofthese compositions reacts with the metal, bonding therewith and forminga thin layer/coating to the surface of the metal. The bonded layer ishard and inhibits corrosion of the metal surface. A range ofphosphate-based formulations may be used to coat and prevent or minimizethe corrosion of metal surfaces.

Processes and articles prepared therefrom disclosed and described hereinovercome many if not all of the problems related to conventionalpassivation processes of steel and other corrodible metals. The instantprocesses also provide a more economical, environmentally-friendlymethod of coating steel and other metal surfaces with acid-baseinorganic phosphate based coatings that not only passivate the layer butalso provide abrasion resistance along with good aesthetics in one step.

Referring now to FIG. 1, which is a representation showing stabilityregions of various phases of iron as a function of pH and the redoxpotential Eh. The black bold curves separate immunity, corrosion, andpassivation regions for steel, where the lower region represents theimmunity region where iron remains in metal form, the left hand side ofthis region is the corrosion region where iron is dissociated into Fe²⁺(aq) ions, and the right hand side representing the passivation regionwhere iron becomes iron trihydroxide Fe(OH)₃.

When phosphating is done according to the conventional processes of dipcoating steel components in a bath of phosphoric acid (or an acidphosphate) and an oxidizer, the steel surface moves from very low pH toslightly higher pH and at the same time, due to presence of theoxidizer, it also moves to a higher Eh point (see line 1). In theprocess, it passes from the region of corrosion to passivation and thesurface is converted from a corrosive layer to a passivating layer. Thispassivation layer is essentially that of iron phosphate (FePO₄),magnetite, and iron hydroxide (Fe(OH)₃). The surface is generally porousand smooth and therefore needs a coating to plug in the porosity inorder to protect the passivated surface completely from atmosphericcorrosion. This also represents the process in which an oxidant, such aspotassium permanganate, is used. Conventional polymeric coatings can becharacterized as moving the steel surface from the corrosion region topassivation region by oxidizing the steel surface to Fe(OH)₃. However,the passivation layer formed from this process is fairly close to theregion of corrosion for steel and thus, explains at least in part, someof the inferior characteristics of this method.

In contrast, the process disclosed and described herein is based on aninorganic phosphate coating produced by acid-base reaction of an acidicphosphate and a metal oxide or metal hydroxide, or oxide mineral. Sincethe instant process is essentially based on an acid-base reaction, theend reaction product is near neutral, and the pH of coatings preparedtherefrom are believed to be between 8 and 9, which is furtherpositioned in the passivation region as shown in FIG. 1. In certainaspects, there is present an excess of alkaline precursor (e.g.,magnesium hydroxide) distribution in the coating that has not reacted,which is believed beneficial in raising the pH of the coating beyond 7to further position the coating in the passivation region as representedin FIG. 1.

Due to sufficiently high pH of the instant coating formulations, steelsurfaces will likely remain in the pH range of passivation region (wellabove pH=6). Thus, the instant coatings can protect against intrusion ofacidic solutions, at least in part due to the excess Mg(OH)₂ present,which can function as a buffer to protect steel from corrosion. Theinstant coatings are superior to current commercial coatings containingzinc hydroxides with regard to buffering capacity, because zinchydroxide is not stable below pH of 5. Thus, zinc oxide coatings canplace steel substrate in the corrosion region in acidic environments.Moreover, based on lower electrode potential of magnesium(Eo^(Mg+2)=−2.37V) verses zinc (Eo^(Zn+2)=−0.7V), either in low pHenvironments or reduction environments, magnesium-based coatings, asdisclosed herein, will provide better protection than zinc-basedcoatings. Protection of steel in the reduction environment using theinstant coatings is beneficial for applications requiring hightemperatures, such as waste to energy incinerators, turbines, in anyhydro carbon combustion environment, and in some chemical processes.

The instant coatings disclosed herein can comprise, in part, theformation of poly phosphates, and in particular, poly phosphates formedby phosphites at the interfacial regions of the substrate surface in theinstant coating. Polyphosphate can provide abrasion resistance andimpermeablity to water and humidity, thus improving abrasion resistanceas well as improving corrosion resistance to the substrate surface.

In one aspect, an acid-phosphate composition, one acidic with a pHbetween about 3 to about 4.5, and the other, an alkaline component witha pH between about 10 and about 11. These two components are contactedwith the substrate surface, where they combine form a coating. Forexample, mono potassium phosphate (KH₂PO₄) and a magnesium hydroxide(Mg(OH)₂, or its brine) composition with or without fillers such aswollastonite (CaSiO₃) or fly ash, can be combined and contacted with acorrodible metal surface (e.g., steel). Once the compositions contactthe surface, a coating forms that bonds instantly to the substrate.While not wishing to be held to any particular theory, it is believedthat the contact by the acidic phosphate and an alkaline oxide orhydroxide, or oxide mineral components provides an initial passivationlayer (sub-, primer, or bottom layer) as well as the corrosionprotective layer.

Line 2 in FIG. 1 shows at least in part, a typical result of the processdisclosed and described herein. In a first step of the instant process,when the mixture of the acid and base is sprayed on the substrate, theacid solution lowers the pH of the substrate. At this point, most if notall of the chemical reactions that occur in the commercial dip coatingalso occur in the instant process as the first step. However, in thesubsequent acid-base reaction, reaction products such as magnetite, oriron hydroxides, react with the phosphate and form iron phosphate. Theacid base chemistry of the instant process increases the pH toapproximately 8, and in turn, drives the steel substrate pH beyond thecorrosion region to the passivation region. In addition, the instantprocess also produces a phosphate-based abrasion resistant coating, thusresistant to both corrosion and abrasion. Therefore, the instant methodeliminates the need for baths of acid solution, sludge to be disposed,the regimental time frame for dipping and drying, and after-coating ofthe steel.

First Component—Acid Phosphate Precursor Material

Acidic Phosphate Component

The acidic phosphate component consists of phosphoric acid and/or anacid-phosphate of formula, A^(m)(H₂PO₄)_(m).nH₂O, where A is an m-valentelement such as sodium (Na, m=1), potassium (K, m=1), magnesium (Mg,m=2), calcium (Ca, m=2), aluminum (Al, m=3) etc. A may also be a reducedoxide phase when higher-valent oxides are used. For example, for iron,which exists in valence state of +2 and +3 (FeO and Fe₂O₃ as oxides), Acan be the metal of lower oxidation state. It can also be a cation ofoxides of four-valent metal oxide such as ZrO²⁺, in which case m=2. nH₂Oin the formula above is simply the bound water, where n can be anynumber, normally ranging from 0 to 25.

It is possible to use hydro phosphates of trivalent metals such asaluminum, iron and manganese represented by the formula AH₃(PO₄)₂.nH₂O,where A is a transition metal that includes aluminum, iron, manganese,yttrium, scandium, and all lanthanides such as lanthanum, cerium, etc.

In case the pH of the acidic precursor is higher than needed for instantreaction, phosphoric acid may be added and the pH may be adjusted tobring down the pH. A preferred pH selected is between 3 and 4, and themost preferred pH is between 3 and 3.5. either elevating the pH ofphosphoric acid or that of an acid-phosphate such as magnesiumdihydrogen phosphate (Mg(H₂PO₄)₂) or aluminum trihydrogen phosphate(AlH₃(PO₄)₂) by neutralizing partially using an alkaline oxide,hydroxide, or a mineral, or by acidifying a dihydrogen phosphate such asmono potassium phosphate (KH₂PO₄) that has a pH>3.5 by adding a smallbut appropriate amount of phosphoric acid or a low pH acid phosphatesuch as Mg(H₂PO₄)₂ or aluminum trihydrogen phosphate AlH₃(PO₄)₂.Examples described later in this document provide the art of adjustingthis pH.

Often the acid-phosphate used in the precursor is only partiallysoluble. In such a case, the precursor is wet-milled so that the averageparticle size passes through 230 mesh sieve (less than 70 micron).

For oxychloride and oxysulfate compositions, the acidic componentconsists of magnesium oxychloride, and magnesium oxysulfatesappropriately acidified with either hydrochloric acid or sulfuric acidto reduce the pH.

Water may be added to the precursor component to reduce the viscositythereof, or other types of viscosity reducing agents may be used.Commercial additives that prevent algae growth may also added to thisprecursor so that no algae growth occurs during storage of thisprecursor.

Second Component—Basic Component

Basic Oxides, Hydroxides and Basic Minerals

Basic precursor generally consists of a sparsely soluble oxide, orpreferably a hydroxide with a particle size less than 230 micron. Theoxide may be represented by the formula B^(2m)O_(m) or B(OH)_(2m), whereB is a 2m-valent metal. All divalent metal oxides (m=1), and sometrivalent metal oxides in reduced state fall into this category ofsparsely soluble oxides. Examples of divalent oxides are, but notlimited to, magnesium oxide, barium oxide, zinc oxide, calcium oxide andcopper oxide. Examples of trivalent oxides in reduced state are ironoxide (FeO), and manganese oxide (MnO).

Inorganic Phosphate Coating Compositions

A range of phosphate compositions may be used as the corrosion inhibitorcoatings commensurate with the spirit and scope of that disclosed anddescribed herein, the following four exemplary, non-limiting examplesare provided:

-   -   1. Magnesium potassium phosphate coating formed by the        combination and/or reaction of magnesium oxide (MgO) and mono        potassium phosphate (KH2PO4), which in the presence of water        combine to produce magnesium potassium phosphate cement,        comprising MgKPO4.6H2O. Magnesium potassium phosphate is also        referred to hereafter as “MKP”.    -   2. Magnesium hydrogen phosphate (newberyite) coating formed by        the combination and/or reaction of magnesium oxide (MgO) and        phosphoric acid solution (H3PO4 solution), which when mixed well        and allowed to dry, combine to produce a magnesium hydrogen        phosphate coating comprising MgHPO4.3H2O.    -   3. Magnesium hydrogen phosphate (newberyite) coating formed by        the combination and/or reaction of Magnesium dihydrogen        phosphate compositions usually have an aqueous pH between about        2.5 and about 5.0. MHP solutions with a pH of about 3 or        slightly higher are generally believed more effective in the        production of corrosion resistant products and, for at least        that reason, tend to be preferred. Magnesium hydrogen phosphate        is also referred to hereafter as “MHP”.    -   4. Iron hydrogen phosphate coating formed by the combination        and/or reaction of wustite (FeO) or magnetite (Fe3O4) and        phosphoric acid (H3PO4), which when mixed well and allowed to        dry combine to produce iron hydrogen phosphate coatings        comprising FeHPO4. Iron hydrogen phosphate is also referred to        hereafter as “mono-iron phosphate”, or “MIP”.

Under ambient conditions, magnesium potassium phosphate compositions,magnesium hydrogen phosphate compositions and iron hydrogen phosphatecompositions exhibit a paste-like consistency. When these compositionsare applied to a surface, e.g., steel, as coatings, it is believed thata reaction occurs and a thin layer of the above compositions bonds tothe metallic surface. The remaining parts of the coatings are looselybound and can be easily scraped off, but the thin layer coating is veryhard, resistant to abrasion, and inhibits corrosion of the surface.Thus, this thin layer acts like a primer, protecting the metallicsurface from corrosion. Similar results are observed when thesecompositions are applied to the surface of other metals besides steel,such as aluminum.

Detailed X-ray diffraction studies (see, for example, FIG. 2) ofmagnesium-containing coatings of the instant disclosure appear tocomprise a thin layer of magnesium chromate, which is believed formed asa result of the reaction of chromium from the metal surface andmagnesium oxide/hydroxide from the instant magnesium-containing coating.The reaction may be represented by

MgO+CrO₃→MgCrO₄.

Since the excess overlayer of acidic phosphate/alkaline oxide issomewhat deficient in alkaline oxide content, it does not set at thisinterface and can be easily removed, leaving a thin primer on thesurface, which is well bonded.

It is also possible to independently produce this primer by diluting theacidic phosphate/alkaline oxide, material and then applying the dilutedcoating on the surface. In the case of steel treatment, the thin layeris mostly transparent and it retains the shiny surface and texture ofthe treated steel. Coatings of MKP, MHP or MIP

In another aspect, disclosed and described herein, is a method ofcontacting a rusted (corroded) surface of steel with a compositioncomprising an acidic phosphate and alkaline metal oxide/hydroxide, wherean excess of the composition and a portion of the rust is renderedreadily removable and/or dislodges from the surface, and a thin and hardcorrosion protection layer is provided on the steel surface. Thus, theinstant coatings disclosed and described herein make it is possible to“clean” a surface of rusted steel and apply a corrosion protection layerat the essentially same time.

As discussed above, during the coating of the steel using the instantprocess, it is believed that a primer is formed by the reaction ofchromium from the steel surface and the oxide from the coating.Therefore, in one aspect, an oxide-rich coating, whereby some of theoxide is used in forming a primer and the rest is used in the reactionthat forms a acid-base phosphate coating, protective(corrosion/abrasion-resistant) coating, is provided. Thus, applicationof a “primer and paint” can be accomplished in just one step (or onecoat), where the primer and/or paint provides corrosion resistance forcorrodible surfaces.

In another aspect, the instant corrosion resistant coatings can beformulated to provide aesthetic properties, such as proper shine andtexture on them. This effect may be achieved, for example, by addingcrushed glass or any other high solubility glass to the instant acidicphosphate/alkaline metal oxide/hydroxide formulations. The resultingcoating comprising crushed glass prepared by the processes disclosedherein is a very dense glassy surface. Additional suitable ceramicpigments may be further added to produce colored paints. Soluble glassin combination with the instant compositions above can also be used informulations for coating of solid objects, to provide very dense, glassysolid coatings having corrosion resistance.

Experimental Section

The following examples are illustrative of the embodiments presentlydisclosed, and are not to be interpreted as limiting or restrictive. Allnumbers expressing quantities of ingredients, reaction conditions, andso forth used herein may be understood as being modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth herein may beapproximations that may vary depending upon the desired propertiessought to be obtained. At the very least, and not as an attempt to limitthe application of the doctrine of equivalents to the scope of anyclaims in any application claiming priority to the present application,each numerical parameter should be construed in light of the number ofsignificant digits and ordinary rounding approaches. Severalexperimental examples, listed below, were conducted in order toformulate, coat, and demonstrate the attributes of the instantcompositions disclosed herein.

EXAMPLE 1 MHP-Based Corrosion Protection Layer

In this Example, MHP (Mg(H₂PO₄)₂2H₂O) was first diluted with water, andcalcium silicate and aluminum oxide were added as fillers to form a thinpaste. The amount of water used in diluting the MHP-based material canvary, depending on the amount of water contained in the material tobegin with (most MHP-based materials are difficult to dry when made and,therefore, usually contain some water.) Preferably, dilution watershould be added in an amount equivalent to about 20% by weight of MHP.The amounts of calcium silicate and aluminum oxide added as fillers toform a thin paste may also vary. In this example, 80 grams of calciumsilicate and 60 grams of aluminum oxide were added for each 100 grams ofMHP. To this mixture, 96 grams of MgO were added for each 100 grams ofMHP. The calcium silicate and the aluminum oxide were mixed for 10minutes each. When the MgO was added the temperature of the paste wasmonitored, and mixed until it reached a temperature of about 85° F. Thepaste was then applied to a well polished steel plate surface and theplate was cured for several days at ambient. After one week, the top(excess) dried layer of the coat could be easily removed, but a thinlayer coating was present on the steel surface, which adhered to thesurface extremely well. Some of the paste had run down to the other sideof the plate and had bonded to the edges of the plate. It was observedthat the uncoated side of the plate had corroded in the center, awayfrom the bonded part along the edges, but a contour of non-corrodedregion remained between the bonded part and the center. It was surmisedthat the paste segregated on the other side and a thin paste seepedbeyond the visible part of the coat on the other side. FIG. 2 shows theX-ray diffraction pattern of this layer on steel, where distinct peaksof magnesium chromate are observed. As discussed above, it is believedthat chromium from the steel reacts with magnesium oxide in the acidenvironment, providing a chemically very stable magnesium chromateproduct, which may contribute in part to the corrosion protectionafforded by the coating.

EXAMPLE 2 Corrosion Protection Layer On Rusted Steel Surface

In this Example, an MKP-based formulation prepared as a paste comprisingcalcium silicate was applied on a rusted surface of steel. The MKP pastewas formed by mixing one part of dead-burnt magnesium oxide (calcined attemperatures higher than about 1,300° C.), three parts of mono potassiumphosphate and six parts of calcium silicate. To this powder mixture wasadded two parts of water to provide a paste. As mixing was continued,the paste cooled by a couple of degrees initially, indicatingdissolution of mono potassium phosphate; but, as magnesium oxide beganto react, the temperature began to rise. Mixing was continued until thetemperature of the paste rose to about 85° F. and, at this point, thepaste was applied to the rusted surface of the steel. When cured, thetop (excess) part of the coat could be removed easily. This hardenedlayer, however, also removed the corrosion (rust) layer from the plate.Surprisingly, a part of the paste had seeped through the rust and hadbonded to the underlying steel surface. FIG. 3 shows various phosphatephases contained in this corrosion preventing layer. Noteworthy is thatthe steel surface did not corrode when kept in humid and hot atmosphere,indicating the acid-base phosphate formation provided a corrosionprotection layer.

EXAMPLE 3 Iron Oxide Based Corrosion Protection Paint

In this example, 165 grams of MHP material were dissolved in 168 gramsof water by mixing and stirring for about one hour. To the resultingsolution was added 16.5 grams of wollastonite (CaSiO₃) passing 200 mesh.The resulting paste was stirred and mixed for about 35 minutes, afterwhich 200 grams of hematite (Fe₂O₃) was added and the paste furtherstirred and mixed for about 15 minutes. 5 grams of magnetite (Fe₃O₄) wasthen added and the paste further stirred and mixed for about 10 minutes.The resulting paste was then painted onto the surface of a polished mildsteel plate. Setting was very slow. There was no detectable heatingduring curing, however, once set, the coating adhered to the steelsurface and could not be removed easily. The coating provided excellentcorrosion resistance to the steel. On this surface a second layer ofphosphate cement, as described in Example 4 below, can optionally beadded.

EXAMPLE 4 Magnesium-Glass Phosphate Composite Formulation

300 grams of mono potassium phosphate, 100 grams of crushed window glassof sand consistency (average particle size of 70 micrometer) and 200grams of water were mixed for about 90 minutes. To this mixture, 100grams of dead-burnt magnesium oxide were added. The paste was mixed forabout 20 minutes, which thickened. The thickened paste was then brushedon the coating described in Example 3, and the remaining paste waspoured in a plastic tray. Both samples had hardened by the next day. Thecoating was well bonded to the primer of the Example 3 and formed anattractive, aesthetically pleasing, shiny (or glossy) coating. The pastepoured in the tray was also a very hard ceramic-like material. Thisceramic sample was cured for an additional one week and X-raydiffraction studies were performed. FIG. 4 shows a section of the X-raydiffraction pattern clearly indicating that MgKPO₄.6H₂O was formed, aswell as several phases of hydrated silico-phosphate minerals. Theseinclude, H₂Si₂O₅, H₂SiO₃O₇, and unhydrated phases SiP₂O₇ and SiO₂. Thiscomposition is unique and can be used in one or more applications, forexample, as an electrical insulator, a glossy paint, and/or a corrosionresistant paint.

EXAMPLE 5 Use of MHP As Corrosion Protective Layer

In this example, a solution of magnesium dihydrogen phosphate material(MHP) was used. MgO was added slowly to water with continuous mixing, sothat all of it became wet. About 20% of the stoichiometric amount of MgOwas withheld from the formulation and the composition was prepared as athin paste. This paste was dried at 50° C. and then heated. The resultwas a set MHP material (Mg(H₂PO₄)₂2H₂O “s-MHP”) manufactured with asubstoichiometric amount of MgO and some heat treatment. The s-MHPmaterial was applied over well polished mild steel and the coated steelplate was placed in sunlight in humid conditions. The surface of thesteel contacted with the s-MHP material layer remained uncorroded, whilesurfaces not covered corroded heavily. The s-MHP material had well seton the surface and could not be dislodged easily. Dorsey

In another test, steel plates were coated with the paste formed by thes-MHP material with additional MgO (stoichiometric excess). The coatingwas hard and dense. X-ray diffraction studies on solid samples made bythis composition showed that the coating contained newberyite(MgHPO₄.3H₂O) and some unreacted magnesium oxide. Some of the pasteseeped to the bottom of the plate along the edges. The plate was put insunlight in a humid environment. The bottom side of the plate corrodedat the center, but there was a contour gap between the central corrodedpart and seeped layer as if the corroded part retreated from the appliedregion. It is perhaps likely that wet material seeped beyond the setlayer and that protected the contoured part from corrosion. Thus, thes-MHP material with added MgO provided a hard, abrasion resistant andcorrosion resistant coating to the steel.

EXAMPLE 6 Methods of Forming Berlinite Coatings on Steel

Theoretical analysis based on thermodynamic principles indicate thataluminum trihydrogen phosphate, if reacted with aluminum oxide(corundum, Al₂O₃), would produce aluminum phosphate (AlPO₄) (berlinite)at about 150° C. Berlinite mineral phase, which is stable up to 1,500°C., would provide a high-temperature coating, and also provide forcorrosion and abrasion resistance for steel and other iron-basedstructural components. Thus, 100 grams of aluminum trihydrogen phosphate(AlH₃(PO₄)₂.5H₂O) viscous paste as disclosed in Example 2, was mixedwith 50 grams of aluminum oxide fine powder and mixed thoroughly to forma thick paste. In preferred aspects, the pH of the paste can adjusted tobetween 3-4 to reduce or prevent formation of a scale layer of ferricoxides that may reduce the coating effectiveness. This paste was brushedon mild steel substrate pre-heated at 175° C. Initially, some waterfraction from the paste evaporated, but the subsequent coating bondedwell to the steel. The entire assembly was maintained at 175° C. forabout three hours. Once all degassing and evaporation had occurred, asecond coat was applied and cured for about three hours at 175° C. Theresulting thick coating formed on the steel surface was hard, dense andextremely well bonded to the steel. X-ray diffraction studies of theformed coating indicated that the coating was essentially berlinite.Thus, the methods disclosed and described herein provides for arelatively simple means for preparing berlinite-precursor formulationsand thereafter forming berlinite coatings useful for providinghigh-temperature protection or improving high temperature service ofarticles, such as steel and other iron-based building materials.

EXAMPLE 7

Wollastonite and water were mixed with the brine to form one stream.Mono potassium phosphate was mixed with water to form the second stream.Both were loaded in two cartridges of a plural spray gun and the mixedstream was sprayed on sandblasted standard steel panels. The measureddensity of this coating was 1.4 g/cm3. The measured abrasion resistanceof this sample was 500 cycles/mil, >4 times that of organic commercialcoatings. The measured bond strength of the coating was 300 psi, >threetimes that of an organic commercial coating.

EXAMPLE 8

Aluminum hydrophosphate was produced by dissolving aluminum hydroxide in50% dilute phosphoric acid solution. Aluminum oxide in three timesexcess to that of the acid solution was then added to this stream andresulting paste was sprayed on standard steel panels. The dried panelwas heated slowly to get rid of all water. It was then heated to 350 F.The dried coating bonded to steel but with lot of cracks. A second coatof the same was sprayed on the first coat, again dried and then heatedagain. The second coat bonded to the first coat, did not crack and theresulting coat was dense and smooth. The measured abrasion resistance:1000 cycles/mil, >8 times that of organic commercial coatings.

EXAMPLE 9

To prove the concept of the material sustaining very high temperature,calcined magnesium oxide and mono potassium phosphate were mixed aspowders in equimolar ratio and were then mixed in water. The resultingpaste set into hard ceramic. It was then heated to 3000 F for threehours. It shrunk 10 vol. %, but was a dense and hard ceramic. Themeasured density of this sample was 2.1 g/cm³

Energy Dispersive X-ray Analysis of Coating

In this test, a mixture of mono potassium phosphate and water (in theratio 2:1 by weight) in one part of a plural spray gun, and magnesiabrine with 61 wt. % magnesium hydroxide and 39 wt. % water in the secondpart of the gun was sprayed on sandblasted steel panels as one stream.The paste formed by the mixture of the two components set as a coatingon the steel surface. The plate was cut vertically to expose the crosssection of the coating. Photographs in FIGS. 5 and 6 show the layers farfrom the substrate and near the substrate respectively. In thesephotographs, the crosses indicate the points of analyses. Tables 1 and 2summarizes the analysis of FIGS. 5 and 6 respectively, of positionsremote and near from the coating-surface interface, respectively, e.g.,elements detected, the wt % and atom % of the coating. The compositionof this coating immediate to the substrate is observed to be richer iniron indicating it is a compound of iron and phosphorous. Potassium andcalcium contents are observed to be lower in this layer, and magnesiumand silicon layers are higher, which indicates the presence of magnesiumsilicate

TABLE 1 Corresponding to FIG. 5. Element Wt % At % O 33.72 50.28 Mg14.72 14.45 Si 04.78 04.06 P 19.13 14.73 K 19.47 11.88 Ca 06.59 03.92 Fe01.58 00.67

TABLE 2 Corresponding to FIG. 6. Element Wt % At % O 40.83 55.71 Mg23.54 21.13 Si 21.90 17.02 P 01.26 00.89 K 02.02 01.13 Ca 00.23 00.12 Fe10.23 04.00

Referring to FIGS. 7 and 8, and Table 3, SEM/EDX data of the same coatedsample as above was tilted and polished to expose different thicknessesof the coating and the steel at the other end. The images show thecoating is comprised of many layers underneath a surface layer. Analysisof the top layer is given in the last column of Table 3 for comparison.Near equal molar content of Mg, K, and P in the top layer indicates thatit consists mainly of MgKPO4.6H₂O. However, distribution of Mg and K arenot the same at different depths. Higher amount of Mg in these layersindicates existence of Mg(OH)₂. Similarly, content of Ca, and Si alsovary indicating non uniform distribution of CaSiO₃. Rodlike structuresin the right hand side micrographs show existence of wollastonite.

TABLE 3 Corresponding to FIGS. 7 & 8. Element Surface layer Average Toplayer O 52.39 51.15 57.1 46.22 46.4 47.91 47.48 52.87 50.19 55.16 Mg17.07 16.56 21.98 30.38 27.79 29.12 14.75 30.56 23.53 14.96 Si 2.09 2.150.88 14.7 14.14 14.29 11.4 1.32 7.62 0.61 P 12.19 12.16 9.2 0.55 2.220.58 7.94 5.09 6.24 15.55 K 8.7 7.92 4.58 0.34 1.08 0.7 4.84 3.43 3.9512.67 Ca 1.1 1.59 0.6 0.16 0.23 0.32 6.25 0.61 1.36 0.53 Fe 6.47 8.475.65 7.64 8.15 7.08 7.34 6.12 7.12 0.53

Vapor Deposition of Corrosion Resistant Coatings

One or both of the acid phosphate or basic components can be vapordeposited, for example from an aqueous solution. This vapor depositionmethod can provide coats at nano- or micrometer thicknesses. Thus, eachcomponent is heated separately to produce vapors. These vapors are thenfunneled into a common tube, so that the vapors are mixed and then aredeposited on the substrate. This coating should form that after reactionon the substrate will mimic the prime coat.

Advantage of vapor deposition methods are, a) thin passivating coats, b)minimum use of material, c) uniformity of coats, d) assembly linecoating, e) automation of the process.

Self Regenerating Coating Process

Referring to FIG. 9, a schematic of self-regeneration of the corrosioninhibiting layer is shown on a surface (10) of iron. With highersolubility of phosphate ions from MgKPO₄.6H₂O compared to that from ironphosphate, any defects (20) developed in the iron phosphate primercoating (40) (as indicated by step 100) can be healed by topcoat (30) ofMgKPO₄.6H₂O as phosphate ions and iron migrate to the defect (asindicated by step 200) and reform (50) the iron phosphate primer coating(40) (as indicated by step 300). Thus, this MgKPO₄.6H₂O top coatessentially heals defects in the thin prime coat on the substrate aftera predetermined time.

Raman Spectra of Coatings

Referring to FIG. 11, All spectra are of coatings next to the substrateexcept the lowest one, which is on a top coat. The peak near 1000 cm−1represents MgKPO₄.6H₂O. The peaks at 1618 cm−1 are identified aspolyphosphates formed by Fe—P═O linkages. These polyphosphates may havechemical bond between the actual coating and the substrate.

1. A method for preventing or reducing corrosion of a corrodible metalsurface, the method comprising contacting the corrodible metal surfacewith a mixture of an acidic phosphate component and a basic componentcomprising at least one of a metal oxide, a basic metal hydroxide, orbasic mineral.
 2. The method of claim 1, wherein the acidic phosphatecomponent is phosphoric acid, alkali metal dihydrogen phosphate MH₂PO₄,alkali earth dihydrogen phosphate M(H₂PO₄)₂ or its hydrate, transitionmetal trihydrogen phosphate MH₃(PO₄)₂ or its hydrate, or mixturesthereof.
 3. The method of claim 1, wherein the acidic phosphatecomponent is mono potassium phosphate or its hydrate.
 4. The method ofclaim 1, wherein the basic component is at least one of magnesium oxide,barium oxide, zinc oxide, calcium oxide, copper oxide, iron oxide, andhydroxides thereof, or magnesium brine containing an effective amount ofmagnesium hydroxide.
 5. The method of claim 1, wherein the basiccomponent is at least one of magnesium oxide and magnesium hydroxide. 6.The method of claim 1, wherein the acidic phosphate component is monopotassium phosphate or its hydrate, and the basic component is magnesiumbrine having a pH of about 9 to about 11, wherein the magnesium brinecontains an effective amount of magnesium hydroxide.
 7. The method ofclaim 1, wherein the mixture of acidic phosphate component and basiccomponent forms at least one of magnesium potassium phosphate, magnesiumsodium phosphate, magnesium hydrogen phosphate, copper hydrogenphosphate, zinc hydrogen phosphate, or iron hydrogen phosphate.
 8. Themethod of claim 1, wherein the surface is steel or aluminum.
 9. Themethod of claim 1, further comprising painting the contacted corrodiblesurface with a magnesium-glass-phosphate paste and providing a hardceramic, glossy coating.
 10. The method of claim 1, wherein thecontacting is with a slurry, paste, spray, or vapor thereof,independently, of the acidic phosphate component or the at least onebasic component.
 11. The method of claim 1, wherein the acidic phosphatecomponent is alkali metal dihydrogen phosphate MH₂PO₄, alkali earthdihydrogen phosphate M(H₂PO₄)₂ or its hydrate, transition metaltrihydrogen phosphate MH₃(PO₄)₂ or its hydrate, or mixtures thereof, andwherein the basic component is at least one of magnesium oxide, bariumoxide, zinc oxide, calcium oxide, copper oxide, and hydroxides thereof,or magnesium brine containing an effective amount of magnesiumhydroxide, further comprising wollastonite (CaSiO₃) or crushed or highlysoluble glass.
 12. The method of claim 1, wherein the acidic phosphatecomponent is mono potassium phosphate or its hydrate, and wherein thebasic component is magnesium brine having a pH of about 9 to about 11,wherein the magnesium brine contains an effective amount of magnesiumhydroxide, further comprising wollastonite (CaSiO₃) or crushed or highlysoluble glass.
 11. The method of claim 1, wherein the acidic phosphatecomponent is alkali metal dihydrogen phosphate MH₂PO₄, alkali earthdihydrogen phosphate M(H₂PO₄)₂ or its hydrate, transition metaltrihydrogen phosphate MH₃(PO₄)₂ or its hydrate, or mixtures thereof, andwherein the basic component is at least one of magnesium oxide, bariumoxide, zinc oxide, calcium oxide, copper oxide, and hydroxides thereof,or magnesium brine containing an effective amount of magnesiumhydroxide, further comprising wollastonite (CaSiO₃) or crushed or highlysoluble glass.
 12. The method of claim 1, wherein the acidic phosphatecomponent is mono potassium phosphate or its hydrate, and wherein thebasic component is magnesium brine having a pH of about 9 to about 11,wherein the magnesium brine contains an effective amount of magnesiumhydroxide, further comprising wollastonite (CaSiO₃) or crushed or highlysoluble glass.
 13. The method of claim 1, wherein the acidic phosphatecomponent is mono potassium phosphate or its hydrate, and wherein thebasic component is magnesium brine having a pH of about 9 to about 11,wherein the magnesium brine contains an effective amount of magnesiumhydroxide, further comprising wollastonite (CaSiO₃) or crushed or highlysoluble glass. The corrosion-inhibiting coating of claim 12, wherein thetotal amount of hematite used is greater than the amount of magnetite orwustite.
 14. A method comprising contacting a corrodible surface withcoating consisting essentially of a mixture of magnetite or wustite, andhematite; with a solution of phosphoric acid or magnesium dihydrogenphosphate, wherein the corrodible surface is essentially without aprimer layer; and providing a corrosion-inhibiting coating, the coatingcomprising iron hydrogen phosphate.
 15. A method of providing corrosioninhibition comprising: providing a combination of at least one of thefollowing: (i) magnesium oxide (MgO) and mono potassium phosphate(KH₂PO₄); (ii) magnesium oxide (MgO) and phosphoric acid solution (H₃PO₄solution); (iii) magnesium oxide (MgO) and magnesium dihydrogenphosphate; (iv) ferric oxide (Fe₂O₃) and phosphoric acid (H₃PO₄); (v)magnesium brine containing an effective amount of magnesium hydroxideand mono potassium phosphate (KH₂PO₄); (vi) magnesium brine containingan effective amount of magnesium hydroxide and phosphoric acid (H₃PO₄);or (vii) magnesium brine containing an effective amount of magnesiumhydroxide and magnesium dihydrogen phosphate; and contacting the surfaceof a corrodible metal with at least one of the combinations (i)-(vii).16. The method of claim 15, wherein the combination is presented as aslurry, paste, spray, or vapor.
 17. An article comprising acorrosion-inhibiting coating formed by the combination of an acidicphosphate with a basic metal oxide or basic metal hydroxide.
 18. Thearticle of claim 17, wherein the coating is at least one of magnesiumpotassium phosphate, magnesium sodium phosphate, magnesium hydrogenphosphate, barium hydrogen phosphate, copper hydrogen phosphate, zinchydrogen phosphate, or iron hydrogen phosphate.
 19. The article of claim17, wherein polyphosphates are present at the interface of the articlesurface and the corrosion-inhibiting coating.
 20. The article of claim17, wherein magnesium chromates are present at the interface of thearticle surface and the corrosion-inhibiting coating.
 21. The article ofclaim 17, having a coating comprising a berlinite phase (AlPO₄)detectable by x-ray diffraction. 22-25. (canceled)
 26. A methodcomprising contacting a metal surface, at least a portion of the metalsurface being corroded, with a composition comprising a mixture of anacidic phosphate component and a basic component of at least one ofmetal oxide, metal hydroxide, or basic mineral; bonding at least aportion of the composition to the corroded metal surface and the metalsurface; wherein at least a portion of the composition and a portion ofthe previously corroded surface is removable and/or dislodges from themetal surface removing at least a portion of both the corroded metalsurface and the composition; and forming a thin, corrosion protectionlayer on the surface, wherein the thin, corrosion protection layer is atleast one of magnesium potassium phosphate, magnesium sodium phosphate,magnesium hydrogen phosphate, barium hydrogen phosphate, copper hydrogenphosphate, zinc hydrogen phosphate, or iron hydrogen phosphate.